1. Field of the Invention
The present invention relates to a semiconductor light emitting device in which at least an active layer and a cladding layer on a substrate are made of II/VI-compound semiconductors.
2. Related Art
Since it is desired that optical discs and magneto-optical discs be recorded and/or reproduced with high density and high resolution, the demand for a semiconductor laser which emits green or blue laser light has increased.
II/VI-compound semiconductors made of group II elements such as Zn, Hg, Cd, Mg and group VI elements such as S, Se, Te are promising materials for forming semiconductor light emitting devices such as semiconductor lasers, light emitting diodes or the like. In particular, ZnMgSSe mixed crystal can be grown on a GaAs substrate and is suitable for use as a guiding layer and a cladding layer for fabrication of a blue semiconductor laser (see "Electronics Letters 28 (1992) p.1798").
When this kind of a II/VI-compound semiconductor light emitting device such as when a ZnMgSSe compound semiconductor is formed as the cladding layer, a GaAs substrate and a ZnSe substrate are used as the semiconductor substrate on which the cladding layer and the active layer are epitaxially grown because they have excellent crystallinity and are now commercially available on the market. In this case, in order that the semiconductor light emitting device may efficiently emit laser light with a desired shortwave frequency, the cladding layer that is eptaxially grown on the GaAs substrate directly or via a buffer layer should be formed as a compound semiconductor layer with excellent crystallinity.
Therefore, semiconductor light emitting devices have previously been considered wherein a lattice constant of the cladding layer is in strict agreement with that of the GaAs substrate. For this reason, values x and y of the Zn.sub.x Mg.sub.1-x S.sub.y Se.sub.1-y cladding layer were selected to be in strict agreement and compositions could not be selected freely. Thus, the semiconductor light emitting devices could not be fabricated satisfactorily.
Moreover, in the known II/VI-compound semiconductor light emitting devices, a p-type electrode obtained when a semiconductor laser using an electrode formed on the opposite side of the substrate, particularly, when an n-type substrate is fabricated generates much heat and the luminous intensity is therefore deteriorated.